Liquid damped telescopic shock absorber



May 2, 1944. P. w. THORNHILL LIQUID DAMPED TBLESCOPIC SHOCK ABSORBER Filed Feb. 25, 1945 CV1? A41 Patented May 2, 1944 LIQUID DAMPED TELESCOPIC SHOCK ABSORBER Peter Warborn Thornhlll, Leamington Spa, En

land, assignd or to John Henry Onions, Coventry, Englan Application February 25, 1943, Serial No.

In Great Britain February 20, 1942 7 Claims.

This invention relates to liquid damped telescopic shock absorbers, more particularly shock absorbing struts and it has ior an object to provide an improved form and arrangement of damping valve device, which is adapted to damp the recoil movement of the shock absorber in a simple yet efilcient manner.

It is a further object of the invention to provide an improved construction of telescopic shock absorber in which provision is made for one of the telescopic members to rock laterally within the other, thus enabling one ofsaid members to be fixedly mounted upon a vehicle or aircraft, while the other is pivotally attached directly to an anguiarly movable arm by which a wheel or'equivalent is carried. A shock absorber of this general form is described in our co-pending application 472,042, filed January 11, 1943.

According to the invention there is provided a liquid damped telescopic shock absorber comprising a cylinder, a hollow plunger having a pistonhead arranged to slide longitudinally within the cylinder, a recoil piston slidable within the plunger, a tubular stem anchoring the recoil piston to the end closure wall of the cylinder, the passage through said stem serving as' a liquid connection,- which extends from the cylinder to that plunger space beyond the recoil piston and which restricts the flow of liquidi'rom the cylinder to the said plunger space when the shock absorber is being shortened, thereby damping the shorteningmovement, and a damping valve which is incorporated in the piston head so as to Open easily and allow liquid to flow freely from the cylinder to the plunger during shortening of the shock absorber, but to close during jecting flange which extension of the shock absorber, thus restricting the flow of liquid from that plunger working space adjacent the piston head, back into the cylinder, and thereby damping the extending movement of the shock absorber.-

Further, in a liquid damped telescopic shock absorber in which a tubular plunger member hav ng a piston head at its inner end rocks relative to a cylinder as the piston head slides within the cylinder, ast'em. secured at one end to the cylinder being arranged to extend through the piston head and carry a recoil piston which slidably engages with the interior of the plunger, the present invention is characterised by the fact that the said piston head is fitted with a dampclamped or otherwise secured around ing valve to allow free flow of liquid from the cylinder to the plunger but not vice versa, the stem having a longitudinal passage which forms interior of the plunger at that side of the 'recoil piston remote from the piston head. The

piston head is preferably formed with an aperture through which the stem passes with considerable clearance, to allow for lateral movement of the stem as a resultof rocking of the plunger. Also the damping valve may advantageously comprise an annular valve member which is slidable longitudinally upon the stem and radially with respect to the piston head, whereby the valve member is adapted to close the relatively large aperture for the passage of the stem through the piston head, despite lateral movement of the stem relative to said piston head due to rocking of the plunger in the cylinder. Conveniently the valve member is mounted with lateral freedom upon a pliirality of pins which latter carry springs arranged to press the valve member against the surface of the piston head. Furthen'the stem may be attached to the end wall .of the cylinder by cushionrmeans enabling the stem to move laterally within the cylinder as the plunger rocks, the end of the stem conveniently being provided with an outwardly prois located between a pair of cushion members. v n The invention is illustrated by way of example in the accompanying diagrammatic drawing. in which: f

Figure 1 is a side elevation. partly in section, showing the general arrangement of a shock absorbing strut suitable ior incorporation in th landing gear of an aircraft; and Figure 2 is a fragmentary sectional elevation of the damping valve drawn to an enlarged scale.

The shock absorber shown in Figures 1 and 2 comprises a tubular cylinder ll, the upper end of which is closed by a plug. member H formed with a lug It, by which latter the'cylinder is adapted to be secured to an aircraft or vehicle body, a second fixing lug I! being provided at the lower part of the cylinder it so that the latter can readily be mounted in a rigid manner. The lug i3 is formed upon a sleeve ll, which is the cylinder I0 so as to constitute a s'upportmr a bracket IS. A tubular plunger I8 is arranged to wall l1 having a pair of lugs l8 perforated to receive a spindle is upon which a block 20 is pivotally mounted. The block 20 is.drilled at right for the eception of a subjected to appreciable axial-loads. v

the plate 28 and packing-ring together seal the :ei'rtent.

-1lange32, which is .disposed'between a pairof annular cushion'membersfl and 34 conveniently *arrangement being such that the stem ii is adapted to swing 'or'rock within limits relative to 'The'oppqeiteendpf the arm 22 is pivoted-to the lowerpart of therbracket I! by a pinorequiva lent 24. Thusas the wheel or equivalent moves vertically, 'due to a landing shock or to inequalities in the surface over which the aircraft or ve hicle is travelling, the arm 22 is caused to move angularly about the pin 24, thus moving the plunger member I 9 telescopically up and down; within th cylinder it, this movement being accomplished by aislight lateral rocking owing to the 'arouate path whichis'followed by the second spindle 2l. The block", serving as the con nection between the plunger member i9 and the arm 22, functions in the manner. of a universal joint serving'to reduce the'operating friction in the various pivots,.1eyen .when thewheel axle I3 is At its upper. end the .;.-plunger"-member I8 is formed or provided with-a wsbm'ewhat barrelshaped piston heads-2B, which isadapted to slide .in a substantially' liquid-tight manner within the cylinder I I owing to" the provision-of a pair of resilient packing rings 29, the curved shape of the piston head Zigenabling the'latter to tilt within the cylinder as the plunger member I! .grocks, as/above described. Downwardmovement of the'plunger member 18 is limited by a stop projection 21 formed within the cylinder-Ill for -;ens sement with the under-surface of the piston Moreover an annular plate 29 is arranged to have substantial radial freedom within a housing '29, and is vtitted witha packing ring Ill :oi felt, or other .soft material through which the plunger member i6 is arranged to slide; thus lower end of the cylinder iii against theadmission 'of dirt and foreign mattenat-the same time permittir' 'gthe plunur member iito slide axially, as well as rock in a radial sense, to the requisite v../ A tubular stemll is disposed within the'cylinder II and has its up end anchored in aIsomewhat, resilient manner to the plug v6| l. 'For this purpose the stem 3] is formed. ith a radial composed of soft rubber. These cushionimembers are located within a cavity formed in the .plug

ascenso sorber. The plate ll is substantially smaller in diameter-than the'interior of the plunger member ll, and in order to allow said plate to move radially so as to compensate-for rocking movements of the stem 9| relative to the pistonhead l5, saidplate is formed with aplurality of holes '40 through which pass a plurality of; pins 4| secured to the iston head by means such as the screw threading indicated at 42. The holes 40 are considerably larger than the pins 4i so as to allowfor the above-mentioned radial movement of the plate 38. held in position by washers 44, normally keep the Springs 49, which are plate 39 pressed against the under surface of packing ring 41, is freely slidable within the Ii andareheld in position bya gland nutfl, the v the axis of the cylinder ill,"but is located against substantial axialzinovement; At. its lower end the stem is formedwitha recoil piston arranged :to be a relatively close sliding fit withinthe plunger member IS; the periphery of the recoil damping piston 36 is-of small axial width so that the piston can rock relative to the plunger memher without causing binding. Thepiston head 25 is formeqwith arelatively large central aperture 31, through which the stem ii is arranged to pass, butthis aperture is normally closed by an annular plate 3! constituting a damping valve member. As willrbe seen more clearly from Figure 2,..the internal edges of ,the plate 38 are chamfered, as indicated at 99, so;.that.said plate slides cylinder space -5 I.

the piston head 25, although said plat is able to move downwards upon the pins 4i and thus ward direction through the aperture ll, as will be hereinafter explained. v

'A'floating piston 49, provided with a fluid-tight plunger member I; thus the interior of said plunger-member is divided by the recoil piston 99 and floating piston 48 into three working spaces, which are indicated at.49, 49 and Hirespectlvely. The spaces 48 and 49 are completely filled with damping liquid, whlchlatter also extends through the stem 3i and fills the working space SI of the cylinder ll. A plurality of constricted apertures 52 are formed in the upper part of the-stemil and constitute a means of communication between the plunger space 49 and the The damping liquid is, of course, inserted after assembly through a passage :93, which is closed by s'screwe'd plug 44. The

plunger space 50 is filled with compressed air or other. gas; conveniently pumped in througha valve fitting indicated at I5, thepressure, of course, being arranged to suit the axial load which the shock absorber is intended to sustain.

, The operation of the shock absorber is as follows. When the wheel or equivalent encounters a bump the plunger member 16 is forced upvwards within the cylinder [0, the result being that the volume of the working space I is reduced and that of the working space in the plunger tube is increased, but to a lesser extent, depending p n the relative cross-sectional-areas of these two working spaces. Therefore some of the liquid so from the working space 5| flows through the aperture 31, and by depressing the plate 88 is able to flow relatively freely into the working space 49. The remainder of, the liquid ejected from the working space ii is forced through the apertures 52 and then flows along the stem 3i into the working space 49. The floating piston 49 is,

of course, forced downwards owing to the increase in volume of both of the working spaces 48 and 49, and the pressure of the air in the during the extension or recoil of the shock ab- 15 space 50 is consequently raised, as is quite well known in connection with shock absorbers of the oleo-pneumatic type to which the present invention belongs. when the end of the initial shortening stroke is reached, the pressure of the air in-the working space Sills much greater than that necessary to support the actual load on the shock absorber, and therefore the latter tends to extend to its normal length. This movement is. however, heavily and positively damped owing to. the fact that the liquid which is trapped within the working space 48 can only escape at a relatively slow rate through-the narrow annular passage betwen the interior of the plate 38 and the stem 3i; during this movement liquid flowing from the working space 49 back into the working space 5| of the cylinder i only lightly damped by the apertures 52, thus ensuring that the working space 5| is maintained completely full of liquid.

The invention is of particular utility in cases where the cross-sectional area of the plunger space is substantially smaller than the effective cross-sectional area of the cylinder, the quantity of liquid thus transferred through the stem for any given telescopic movement being dependen upon this difl'erence in area.

The invention thus provides a simple but reliabl and efiicient shock absorber which is easy to install, and in which the outward movement of the plunger is positively resisted by a body of trapped liquid which can escape only gradually through restricted orifices. The arrangements described are, of course, to be regarded as examples only, for various modifications may be made in the construction and design of the par so as to suit requirements.

What I claim is:

1. A liquid damped telescopic shock absorber comprising a cylinder having an end closure wall, a hollow plunger having an apertured piston head arranged to slide longitudinally within said cylinder, 3, recoil piston, a tubular stem anchored to the end closure wall of said cylinder, passing through the aperture in said piston head and sup porting said recoil piston within the hollow plunger for relative sliding movement, means for establishing fluid connection between the working space of said cylinder and the interior of said hollow stem adjacent the point of anchorage of the latter, the hollow stem serving as a liquid connection which extends from the cylinder to the hollow 'plunger at a point beyond the recoil piston, said recoil piston blocking communication from the working space of the hollow plunger beyond it and the working space of the hollow plunger between it and said piston head, a resiliently loaded floating piston in said hollow plunger acting toward said recoil piston in the working space of the hollow plunger therebeyond, and an annular damping valve mounted on said piston head and adapted to restrict liquid flow from said hollow plunger to said cylinder through the aperture in said piston head upon relative movement of the piston head and the end closure wall away from one another while permitting flow of liquid from said cylinder into said hollow plunger through said piston head upon relative movement of the latter toward the end closure wall, whereby the extending movement of the shock absorber is clamped.

2. A shockabsorber comprising a cylindefhaving a closed end adapted for attachment to one part of the load, a hollow plunger extending from the other end of said cylinder and adapted for attachment to the other part of the load, a piston head rigid with said plunger but mounted for limited universal movement in said cylinder, said piston head having an opening therein establishing communication between the interior of the plunger and the cylinder working space, a recoil piston, a tubular stern, means anchoring an end of said stem to the end closure wall of said cylinder for limited universal movement, said stem passing through the aperture in said piston head with considerable clearance and supporting the recoil piston within the hollow plunger, said tubular stem being, adjacent its anchored end, in restricted communication with the working space of said cylinder, an annular check valve controlling fluid fiow through the annular space defined by the exterior of said stem and a portion 01 the piston head defining the aperture therein, and means mounting said valve for axial movement upon the stem and tor radial movement relative to-the piston head whereby the valve member is adapted to close the relatively large aperture for the passage of the stem through the piston head, despite lateral movement of the stem relative to said piston head due to rocking of th plunger in the cylinder.

3. A shock absorber as claimed in claim wherein said annular valve is provided with a plurality of sub-marginal apertures and wherein the means mounting said valve comprises a plurality of pins extending from said piston head through said sub-marginal apertures, and a spring on each pin urging said annular valve into seating position against the underside of said piston head whereby upon compression or said shock absorber the valve will be opened against the thrust of the springs while upon extension thereof the springs will bias the valve to closed position.

4. A shock absorber as, claimed in claim 2 wherein the means anchoring an end of said stem to the end closure-wall of said cylinder comprises a pair of cushion members receiving therebetween a radial flange-extending from said tubular stem.

5. A shock absorber as claimed in claim 2 wherein said stem is provided withan outwardly projecting flange at its end remote from the recoil piston and wherein the means anchoring that end of said stem to the closure wall comprises a pair of annular resilient members disposed on either side of the stem flange, and means for compressing said resilient members to support said stem for limited universal movement.

6. A shock absorber as claimed in claim 2 wherein the periphery of the recoil dampin piston is axially narrow to permit rocking or the plunger relative to the piston. Y

7. A shock absorber as claimed in claim 2 wherein the hollow plunger is connected to the load by an arm which moves angularly about an axis fixed with respect to the cylinder.

PETER WARBORN 'IHORNHILL. 

